1. Field of the Invention
This invention relates to apparatus providing for higher contrast ratios in liquid crystal displays used in the light transmitting mode and more particularly to such liquid crystal displays utilizing optical means for concentrating available ambient light at the rear face of such liquid crystal displays.
2. Description of the Prior Art
Liquid crystal displays used in the light transmissive mode have generally required associated contained light sources to provide the light intensity levels necessary to obtain contrast ratios in the display for satisfactory readability. Transmissive mode liquid crystal displays are generally not utilized in small hand held instruments, since they are capable only of the most inefficient use of available ambient light for providing display contrast. The majority of such instruments using liquid crystal displays are therefore of the reflective mode type, whereby ambient light is passed through the display to the reflector and returned through the display to obtain the necessary contrast ratios for readability. The liquid crystal display assembly when used in the light transmissive mode does not require a backing reflector and therefore has an advantage from the standpoint of requiring fewer parts. There is therefore, a need for a liquid crystal display for use in the light transmissive mode which is capable of efficiently using the available ambient light to the exclusion of self contained light sources.